The read and write head portions of the slider for use in a typical prior art magnetic disk recording system are built-up in layers using thin film processing techniques. In the typical process of fabricating thin film magnetic transducers, a large number of transducers are formed simultaneously on a wafer. After the basic structures are formed the wafer is cut into rows or individual transducers. The magnetic sensor can be any one of various types including tunnel-junction (TMR) and spin valves (GMR). The magnetic transducer 20 is composed of elements that perform the task of writing magnetic transitions (the write head 21) and reading the magnetic transitions (the read head 22) as illustrated in FIG. 1A. The components of the read head 22 are the first shield (S1), the sensor element 25 and the second shield (S2). Separation layer 26 separates S2 from P1 and contributes to the spacing between the read head 22 and the write head 21. The yoke in magnetic transducer 20 includes three pole pieces P1 34, P2 32 and P3 43. P1 has a pedestal pole piece P1P 34P. The P2 32 confronts the P1P 34P across the write gap layer 42 to form the write gap at the ABS. Typically write heads only have one coil layer 37, but two or more coil layers 37, 39 are possible. The P3 43 arches over the resist mound 47. FIG. 1B is an illustration of an enlarged cross section of a prior art magnetic transducer as viewed from the air-bearing surface showing the P2 tip 32T and P1P tip 34T which confront each other across the gap layer 42.
At various stages during the fabrication process chemical-mechanical polishing (CMP) is used to planarize the wafer, achieve desired thicknesses of features. For example, CMP is used to planarize the surfaces of S1, P1, P1P, and P2. Features are typically formed on the wafer by plating through photolithography masks and followed by deposition of refill material over the wafer. CMP is used to planarize the wafer after the refill deposition. The active components in magnetic heads are typically metals such as copper, NiFe, CoFe and CoNiFe. The refill material is typically alumina. The slurry used for CMP conventionally includes an abrasive such as silica or alumina, surfactants, corrosion inhibitors and etchants. Conventionally in preparation for planarization the material for a head component such as shield and pole pieces are deposited significantly thicker than the final target value. Similarly the refill material is also deposited significantly above the final. When the CMP is executed the excess material is removed.
In U.S. Pat. No. 6,554,878 to Dill, et al. a slurry is described for chemically mechanically polishing copper, alumina and nickel iron to a common plane. The slurry includes colloidal silica, potassium and/or sodium persulfate and ammonium persulfate (APS). The concentrations are tailored to chemically-mechanically polish alumina and nickel iron at the same rate or to chemically-mechanically polish the copper at the same rate as the other materials to the same plane.
In U.S. patent application Ser. No. 20020012195 to Lahiri, et al., a P2 pole tip/yoke interface structure in a magnetic head is formed by a process which includes two CMP polishing steps performed on the surface of the write head wafer subsequent to the plating of the P2 pole tip. A refill layer of a dielectric material, such as alumina, is deposited on the wafer surface over the P2 pole tips. The alumina layer projects up wherever the P2 pole tips are formed on the wafer. A first chemical mechanical polishing (CMP) step is next conducted upon the wafer. The first CMP step utilizes a relatively hard polishing pad and a chemical polishing slurry that removes alumina and NiFe at approximately equal rates. The slurry may have a neutral pH with a passivating agent such as benzothiazole (BTA), to a higher pH of approximately 10 where a passivating agent normally is not required. A chemical oxidant may be included in the slurry, and a preferred oxidant is ammonium persulfate. The relatively hard pad preferentially removes the projecting portions and the slurry attacks and removes the alumina and the NiFe that constitutes the P2 pole tip. The first CMP step is conducted until the top surface of each P2 pole tips formed on the wafer is exposed within the polished surface of the alumina layer, as is depicted in The second CMP step of the present invention involves the utilization of a relatively soft polishing pad along with an acidic polishing slurry. An oxidant, such as ammonium persulfate is preferably included in the acidic polishing slurry. The acidic polishing slurry coupled with the soft polishing pad of the second CMP step create an environment in which the P2 pole tip is preferentially attacked as compared to the alumina. As a result, the second CMP step acts to remove the upper surface of the pole tip to form a recessed P2 pole tip surface.
Various nitrides have been proposed as CMP stop layers. In U.S. patent application Ser. No. 2002/0065023 by Siang Ping Kwok suggests using a three layer film, such as nitride/oxide/nitride for a CMP stop layer on the IC chips. In U.S. patent application Ser. No. 20010049183 by Henson, et al., SiC is used as a CMP stop layer.
What is needed is an improved slurry and stop layer for use in fabricating the structures in magnetic heads.